The present invention is especially directed to automotive vehicle network systems, but can also be applied, equally, to stationary self-contained electrical systems; for simplicity, therefore, an "automotive-type" engine is referred to, and the specification will be directed specifically to self-contained networks for automotive use, although the present invention is equally applicable to stationary engines, and connected self-contained networks.
Automotive vehicles customarily use generators, driven by the internal combustion (IC) engine of the vehicle, the generator charging a battery. For starting, a motor is provided, supplied with power from the battery and energized by a suitable starter switch. To provide accurate voltage control, most generators use field structures which are of soft iron so that the degree of magnetism of the field structure can be accurately controlled. A certain remanent magnetism, however, remains and this remanence is used to provide the initial field for the generator upon start-up. The generator, thus, is initially self-excited after the engine has started. The self-excitation should be so reliable, however, that after starting of the engine, the generator can supply power to the on-board network of the vehicle as quickly as possible, particularly since starting places a heavy drain on the battery. The battery, therefore, should be promptly recharged.
It has been found that in many installations the magnetic remanence is not sufficient in order to ensure self-excitation. Various circuits have therefore been provided in order to improve or ensure self-excitation. Most of those circuits and systems are complex. One of such systems uses the circuit including the charge control lamp--usually provided--of the automotive vehicle of which the engine and the control system are a part. Operability and excitation thus will depend on the power capability of the charge lamp and on its operability. Self-excitation becomes increasingly difficult as the air gap of the generator itself increases, and is particularly difficult to obtain in generators not using slip rings. Self-excitation additionally depends on the charge state of the battery, battery voltage, frequency of starting, or attempts to start, and on the other loads already connected to the battery, and thus also loading the generator. Ambient temperature also has effects on the excitation of the generator.